A curve is defined by the parametric equations x = f(t) and y = g(t), where f and g are differentiable functions. Which of the following gives the length of curve C from t = -1 to t = 8?
1) ∫(8 to -1) √(f'(t)² + g'(t)²) dt
2) ∫(8 to -1) √(f(t)² + g(t)²) dt
3) ∫(-1 to 8) √(f'(t)² + g'(t)²) dt
4) ∫(-1 to 8) √(f(t)² + g(t)²) dt